"Common sense" is often wrong. Reality is often counter-intuitive. That the earth is round and yet people can stand at any position on the globe without falling into space is counter-intuitive... but reality nevertheless. It turns out that in areas where science contradicts traditional knowledge or common sense, people are resistant to accepting science. And this seems to be innate - children cannot fully understand the round earth problem that I described above until they are about 8 years old, according to a recent study published in the journal SCIENCE.
Evolution isn't even counterintuitive, but it does contradict the information that many have been spoon-fed by supposed 'authorities' throughout their early development. I guess that's why some of those among us have such a hard time accepting it.